Fibrous structures, such as paper towels, facial tissues, toilet tissues, and board, printing, and writing grades of paper, are a staple of every day life. The large demand and constant usage for such consumer products has created a demand for improved versions of these products and, likewise, improvement in the methods of their manufacture. Such cellulosic fibrous structures are manufactured by depositing an aqueous slurry from a headbox onto a Fourdrinier wire or a twin wire paper machine. Such forming wires are generally an endless belt through which initial dewatering of the slurry occurs and fiber rearrangement takes place. Frequently, fiber loss occurs due to fibers flowing through the forming wire along with the liquid carrier from the headbox.
After the initial formation of the web, which later becomes the cellulosic fibrous structure, the papermaking machine transports the web to the dry end of the machine. In the dry end of a conventional machine, a press felt compacts the web into a single region cellulosic fibrous structure prior to final drying. The final drying is usually accomplished by a heated drum, such as a Yankee drying drum, or a series of can driers for board, printing, and writing grades of paper.
One of the significant aforementioned improvements to the manufacturing process, which yields a significant improvement in the resulting consumer products, is the use of through-air drying to replace conventional press felt dewatering. In through-air drying, like press felt drying, the web begins on a forming wire that receives an aqueous slurry of less than one percent consistency (the weight percentage of fibers in the aqueous slurry) from a headbox. Initial dewatering of the slurry takes place on the forming wire, but the forming wire is not usually exposed to web consistencies of greater than 30 percent. From the forming wire, the web is transferred to an air pervious through air drying belt.
Air passes through the web and the through-air-drying belt to continue the dewatering process. The air passing the through-air-drying belt and the web is driven by vacuum transfer slots, other vacuum boxes or shoes, predryer rolls, and the like. This air molds the web to the topography of the through-air-drying belt and increases the consistency of the web. Such molding creates a more three-dimensional web, but also creates pinholes if the fibers are deflected so far in the third dimension that a breach in fiber continuity occurs.
The web is then transported to the final drying stage where the web is also imprinted. At the final drying stage, the through air drying belt transfers the web to a heated drum, such as a Yankee drying drum for final drying. During this transfer, portions of the web are densifted during imprinting to yield a multi-region structure. Many such multi-region structures have been widely accepted as preferred consumer products. An exemplary through-air-drying belt is described in U.S. Pat. No. 3,301,746.
As noted above, such through-air-drying belts used a reinforcing element to stabilize the resin. The reinforcing element also controlled the deflection of the papermaking fibers resulting from vacuum applied to the backside of the belt and airflow through the belt. Such belts use a fine mesh reinforcing element, typically having approximately fifty machine direction and fifty cross-machine direction yarns per inch. While such a fine mesh may control fiber deflection into the belt, they are unable to stand the environment of a typical papermaking machine. For example, such a belt may flexible enough so that destructive folds and creases occur. Fine yarns do not generally provide adequate seam strength and can burn at the high temperatures encountered in papermaking.
There are other drawbacks of other through-air-drying belts. For example, the continuous pattern used to produce a consumer preferred product may not allow leakage through the backside of the belt. In fact, such leakage may be minimized by the necessity to securely lock the resinous pattern onto the reinforcing structure. Unfortunately, when the lock-on of the resin to the reinforcing structure is maximized, the short rise time over which the differential pressure is applied to an individual region of fibers during the application of vacuum can pull the fibers through the reinforcing element, resulting in process hygiene problems and product acceptance problems, such as pinholes.
Standard patterned resinous through-air-drying belts maximize the projected open area, so that airflow therethrough is not reduced or unduly blocked. Patterned resinous through-air-drying belts common in the prior art use a dual layer design reinforcing element having vertically stacked warps. Generally, the wisdom has been to use relatively large diameter yarns, to increase belt life. Belt life is important not only because of the cost of the belts, but more importantly due to the expensive downtime incurred when a worn belt must be removed and a new belt installed. Unfortunately, larger diameter yarns require larger holes therebetween in order to accommodate the weave. The larger holes permit short fibers, such as Eucalyptus, to be pulled through the belt and thereby create pinholes. Unfortunately, short fibers, such as Eucalyptus, are heavily consumer preferred due to the softness they create in the resulting cellulosic fibrous structure.
Additionally, the effect of superimposing a repetitive design, such as a grid, on the same or a different design can also produce a pattern that is distinct from the components of the pattern. This is known to one of skill in the art as a Moire pattern. Such Moire patterns can detrimentally impact the appearance of products produced by such a forming structure by having unintended designs appear upon the product. These unintended Moire designs are likely to be distinct from any of the patterns used to generate the forming structure.
Accordingly, there is a need to provide a forming wire that reduces fiber loss and non-uniform fiber distribution in specific areas of the resulting product. Such a forming wire should provide a patterned resinous papermaking belt that also overcomes the prior art trade-off of belt life and reduced pinholing. Additionally, the forming wire should provide an improved patterned resinous belt having sufficient open area to efficiently use during manufacturing. Also, the papermaking belt should provide for a patterned resinous belt that produces an aesthetically acceptable consumer product comprising a cellulosic fibrous structure by eliminating Moire patterns resulting from the papermaking process.